I’m trying to set up a simple scene to get the velocity pass so I can use it in postproduction, but the velocity pass is very strange (VRay GPU) or totally missing (VRay CPU).
I create a scene with a teapot (~0.1 m width) that moves 1,1 m (from side to side of the camera view) along the y-axis in 24 frames. In the first and the last frame of the animation, the teapot has keyframes to define the start & end positions:
Since I don’t know the max velocity value, I have to guess it and, In order to see something in the render channel, I have to apply a max velocity value of 0.0001.
Rendering with VRay GPU, the velocity image is far from a smooth color gradient (it applies for both progressive and bucket samplers):
I’ve tried enabling the motion blur in the physical camera and the velocity pass is still appearing blank in VFB (both CPU and GPU rendering).
I attach here a ZIP file that contains two blend files (VRay 7.40; Blender 5.2). One file contains a scene with an object moving in front of a still camera. The other one is a still object in front of a moving camera. Both are two short sequences of 24 frames.
Thank you for the response. Could you please switch to animation from a single frame? Also, check if the motion blur option is enabled with the physical camera. When rendering with interactive render, motion blur will be disabled by default.
thank you very much for the clarification and the modified example files. They were several things to keep in mind (CPU rendering, render animation & motion blur in physical camera). Now, once I have the understanding, I’m able to replicate it and make it work from scratch.
Just as a note: it seems to only work when rendering on CPU (which is totally fine, since it’s blasting fast!).
